The present invention relates to a flow control system in a tobacco shredding machine or the like and more particularly to a flow control system for mantaining constant the flow rate of raw material shredded by a tobacco shredder or the like.
Generally, in a tobacco shredding machine, tobacco leaves, as the raw material, are conveyed to a shredding port provided in front of two upper and lower press conveyors, while being compressed by those conveyors, and are shredded by means of a rotary drum cutter which is rotating in close proximity to the shredding port.
The tobacco leaves thus shredded are delivered to the step which follows the shredding step by the shredding machine, namely, the drying step, the perfume adding step or the mixing step. In this case, maintaining constant the flow rate of the shredded tobacco leaves being delivered to the subsequent step is very important for various purposes, for example, not only for stabilization of the quality of shredded tobacco leaves but also for reduction of load variations in the drying step, for uniform addition of perfume and improvement of the mixing accuracy.
To this end, in the shredding machine and its peripheral equipment, various flow control systems have heretofore been proposed, which are classified into the following three systems.
According to the first system, the flow rate of tobacco leaves entering the shredding machine is kept constant, as proposed in Japanese Patent Application Laid Open Publication No. 118898/76 and Patent Application Publication No. 45185/80.
According to the second system, the flow rate of tobacco leaves which have been shredded by the shredding machine is measured by a continuous weighing machine, and the measured signal is fed back to the shredding machine to directly or indirectly control the procesing flow rate in the shredding machine.
According to the third system, as proposed in DT No. 1532062, taking note of the fact that, of upper and lower press conveyors of the shredding machine, the upper press conveyor for pressing raw material at a constant pressure moves vertically according to the amount of raw material. A measuring member for measuring the amount of such vertical movement is attached to the upper side of a shredding port which vertically moves simultaneously with the upper press conveyor. The measurement result obtained by the measuring member is fed to a speed control section of a press conveyor driving device to control the speed of the upper and lower press conveyors to thereby keep constant the amount of raw material extruded to the shredding port.
However, the first and second systems require various equipments and devices in addition to the shredding machine, thus causing problems such as the increase of cost and of installation space.
The third system does not cause such problems as the increase of cost and that of installation space because the shredding machine per se controls the flow rate. However, the density of raw material passing the shredding port varies depending on the strength of compression by the press conveyors, and even at the same strength of compression. A change in the moisture content of the raw material will cause a change in physical properties, such as softness of the raw material and hence a change in density of the raw material under compression. Thus, the control accuracy can be maintained only under limited conditions.